1. Field of the Invention
The present invention relates to an improved process for the production of glycol ethers, and particularly to the production of ethylene glycol ethers by reaction of ethylene oxide with monofunctional aliphatic alcohols. Ethylene glycol ethers are widely used as chemical intermediates and particularly as solvents.
2. Description of the Prior Art
Though various processes are known for the production of ethylene glycol ethers, the only process used industrially involves the reaction of ethylene oxide with monofunctional aliphatic alcohols, such as methanol, ethanol, n-butanol, and isobutanol; see Ullmanns Encyklopaedie der technischen Chemie, 3rd edition, vol. 3, (1953), p. 140. This process is carried out in liquid phase with excess alcohol at high temperatures and pressures.
In general, the reaction is carried out in the presence of suited catalysts, suchc as alkali metal alkoxides, usually sodium alkoxides, sodium hydroxide, tertiary amines, boron trifluoride, antimony pentachloride, and chlorides of bivalent and trivalent metals and the like. Other known processes are carried out in the absence of catalysts so that the problems caused by the separation of the catalyst from the reaction products are avoided; see Ullmanns Encyklopaedie der technischen Chemie, 3rd edition, vol. 3, (1953), p. 141. A further advantage resides in the absence of corrosion due to the catalyst used. In the non-catalytic processes, however, it is necessary to employ more drastic reaction conditions, particularly higher temperatures and pressures than in the catalytic processes.
The reaction of ethylene oxide with monofunctional aliphatic alcohols results in the formation of monoethylene glycol ether, diethylene glycol ether, triethylene glycol ether, and homologues having higher molecular weights. After the reaction is completed, the excess alcohol is removed and the various ethylene glycol ethers produced are then fractionated.
In the known processes the ethylene glycol ethers are produced either continuously or by batchwise operation. In the former case, normally reactors having an elongated shape, generally tubular reactors, are used, and the ethylene oxide may be fed in partly at one or more points located along the body of the reactor.
The problems that arise in the known processes for the production of ethylene glycol ethers by reaction of ethylene oxide with monofunctional aliphatic alcohols are essentially those relating to the reaction yield and the purity of the product obtained and those relating to the composition and distribution of the various ethylene glycol ether homologues in the reaction products. In the processes of the prior art, yields of ethylene glycol ethers higher than 90% with respect to the ethylene oxide fed in and the alcohol converted are rarely obtained. On the other hand, it is important to minimize the formation of triethylene glycol ether and of the higher homologues, since monoethylene glycol and diethylene glycol ethers are the industrially most important products of the homologue series. For this reason, a large excess of the monofunctional aliphatic alcohol is used in the known processes. However, this leads to the formation of reaction products containing predominantly monoethylene glycol ether and only small amounts of diethylene glycol ether, which is undoubtedly a disadvantage, in view of the demand for both of these products.
On the other hand, lower ratios of ethylene oxide to alcohol in the reaction, while increasing the production of diethylene glycol ether as compared to the monoethylene glycol ether, also lead to the formation of products having higher molecular weights that do not find application in practice. In other words, the known processes are not sufficiently flexible to allow the production of monoethylene glycol ether and diethylene glycol ether in the desired ratios, at the same time avoiding the formation of the undesired products having higher molecular weights.
Moreover, in known processes, ethylene glycol ethers of low purity are obtained, particularly because it is difficult to completely remove the excess alcohol from the reaction products.